In using iron pipe large enough to furnish the amount of water required, due regard must be paid to friction in the pipe. In flowing through a pipe of small size, water loses a great deal of head by friction. This friction between the sides of the pipe and the water, which must be duly considered in a pipe of small size, increases very rapidly as the velocity of the flow increases. It is always a great temptation to use a small pipe, since the cost of the pipe increases rapidly as the diameter increases, but it is penny wise and pound foolish to lay a line of pipe several thousand feet long to furnish water to a house and find when completed that the amount of water furnished by the pipe is on account of friction only a small dribble. In a previous chapter we estimated that the flow of water, in order to furnish three faucets at a reasonable rate, ought to be at least two thousand gallons a day or about one and a half gallons a minute, and the effect of a reduced size of pipe on the head necessary to carry a definite amount of water was shown. The cost of cast-iron pipe should not be more than thirty cents per running foot for four-inch pipe and fifty cents per running foot for six-inch pipe. To this must be added the cost of about seven pounds or ten pounds respectively of lead for each joint and the cost of all the labor involved. The price of terra-cotta pipe is much less, as already indicated, so that it is quite worth while to expend some additional effort on making the tile pipe joints water-tight, if it allows the cheaper pipe to be substituted for the more expensive iron pipe. _Pumping._ Although the present methods of securing water for isolated farm buildings will not corroborate the statement it is safe to say that the proper method of obtaining a water-supply is always to make use of a pond or stream at such an elevation that water will flow to the house by gravity, provided this is possible. Only when the conditions are such that a gravity supply is impossible and water from a well or stream at some lower elevation becomes inevitable is pumping properly resorted to.